One probe (500T10 -C) was inserted between the return
and secondary cyclones for 2 h after removal of the sampling
probe for FTIR measurements that was employed during the
first hour. Flue gas temperature close to this probe was
850T40 -C and flue gas velocity 8 T1 m/s. The other probe
(420T10 -C) was inserted after the secondary cyclone for 3 h.
Flue gas temperature there was 750T30 -C and flue gas
velocity 7T1 m/s. Fly ash passing the probes was sampled
(Fig. 1) and particle size distribution was measured with laser
diffraction method. Particle size of fly ash passing the cooler
probe was 2–17 Am. Slightly coarser particles (up to 100 Am)
passed the hotter probe.